This invention relates to the field of visual display systems, more particularly, to digital pulse-width modulated display systems.
Display systems have long given viewers the capability to adjust display characteristics in order to adapt to ambient conditions, adjust for poor quality input signals, compensate for an aging display device, or to suit personal preferences. Two of the primary means for adjustment have been the brightness control and the contrast control.
The brightness control theoretically adjusts the brightness or intensity of the display by changing the amount of light emitted, reflected, or transmitted by the display. The contrast control adjusts the brightness ratio between light and dark areas of the screen. Typically both the brightness and contrast adjustments are implemented by changing either the gain or offset characteristics, or both the gain and offset characteristics, of the image signal path.
Implementation of brightness and contrast controls in an all digital image display system can be difficult. Typically this involves additional hardware such as multipliers or lookup tables to scale the image data. Software can also be used to scale the image data, but this requires additional processing capability.
A method and system of adjusting the intensity of a pulse-width modulated digital display pixel, wherein each pixel is represented by a binary intensity word, and displayed sequentially for a duration dependent on the binary weight of the bit is disclosed. According to one embodiment of the disclosed invention, the display duration of each bit of the intensity word is altered to either increase the duty cycle of the pixel, resulting in increased pixel brightness, or to decrease the duty cycle of the pixel, resulting in decreased pixel brightness. To adjust the contrast ratio of a digital display, the duration of some bits is increased while the duration of other bits is decreased. The disclosed method and system have the advantage of being inexpensive and easy to implement.